The subject matter of this invention is related to the subject matters of inventions entitled "Virtual Tributary Cross Connect Switch and Switch Matrix Utilizing the Same", Ser. No. 283,178, "System for Cross Connecting High Speed Digital Signals", Ser. No. 283,171, and "System for Cross Connecting High Speed Digital SONET Signals", Ser. No. 283,172 all of which are filed of even date, assigned to the assignee hereof, and both of which are hereby incorporated by reference herein.
This invention relates generally to switch components and non-blocking switching networks utilizing a plurality of switch components. More particularly, the invention relates to a switching component designed for use in the construction of non-blocking switching networks which permit the switching of digital signals having a plurality of data rates, including rates associated with at least DS-3, T1, and SONET telecommunication standards.
Several different switching architectures for permitting the connection of a plurality of bidirectional incoming lines to a plurality of bidirectional outgoing lines are well known to those skilled in the art. Examples of different switching network structures are described in Collins, Arthur A., et al., Telecommunications A Time For Innovation, Chapter 2 (Merle Collins Foundation, Dallas, Tex.; 1972). Depending on the particular function of the switch network in a system, it is sometimes desirable to utilize a strictly "non-blocking" switch network; i.e. a switch network which guarantees that any pair of ports which are not connected may be connected via a free path which always exists regardless of the connection state of the other ports. Such a non-blocking switch network is particularly advantageous in applications such as "cross-connect" systems in telephone trunk networks. Among the known architectures for such "non-blocking" switch networks is a "folded Clos" structure which utilizes switching stages. In a folded Clos structure, each stage must have twice as many output ports as input ports, except for the last "reflecting" stage whose ports equal the number of output ports from the previous stage.
In telecommunication systems presently utilized, it is common to have DS-3 trunks comprising twenty-eight T1 lines (DS-3 and T1 being well documented ANSI standards). Central telephone offices receive the DS-3 and T1 lines and use non-blocking cross-connect switches to perform cross-connect functions. These cross-connect functions typically include: connecting between DS-3 signals where the various signals may be carried on lines entering or leaving a building or may terminate on equipment internal to the building; connecting between DS-1 signals where the various signals may be carried on lines entering or leaving a building or may terminate on equipment internal to the building; and connecting between DS-1 signals were DS-1 signals may be contained in a DS-3 signal or on external lines or on internal equipment. Typically, the data being transmitted over the DS-3 trunk is a bipolar signal which was formed at a multiplexer by taking a binary stream and encoding according to the B3ZS (binary with three zero substitution) standard. Thus, the actual signal being switched in the central office is essentially an analog voltage representation of a DS-3 signal, and mechanical analog switches are utilized for accomplishing the switching function. When the data in the DS-3 format reaches its desired destination it is decoded to produce the original binary (digital) stream. Prior to decoding, however, the clock of the signal must be recovered via a clock recovery circuit so that a decision may be made on the value of the incoming information.
With the advent of the new SONET standards, and the existence of DS-3, DS-0, DS-1, and SPT standards, it would clearly be desirable to have a switching architecture which is capable of handling signal data regardless of the standards by which the signal data was formed. Thus, for example, it would be desirable to be able to receive data from a DS-3 trunk and segment the data into various components which might then be sent out over lines utilizing the DS-1, or SPT standards. In fact, such a switching architecture is described and claimed in the previously referenced copending patent application entitled "System for Cross Connecting High Speed Digital Signals" (Docket #TRA-001). As part of that switching architecture, it is desirable to include a non-blocking switching network which can connect any like signals from among a plurality of groups of like signals regardless of speed; i.e. DS-3 connected to DS-3 concurrently with DS-1 connected to DS-1